1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor used in an electrophotographic apparatus, such as a copier duplicator and a laser printer, and also relates to an electrophotographic process cartridge and an electrophotographic apparatus using the same.
2. Description of the Related Art
In recent years, a photoreceptor having a structure called function-separated type, in which a photosensitive layer is separated into a charge generating layer and a charge transporting layer, has been developed and subjected to practical use since it is excellent in sensitivity, repeating stability of sensitivity and electrophotographic characteristics. A electrophotographic photoreceptor having such a structure basically has two layers, i.e., a charge generating layer having a charge generating material dispersed or dissolved in a binder resin, and a charge transporting layer having a charge transporting material dispersed or dissolved in a binder resin. The charge transporting layer contains, in many cases, a hole transporting material and a thermoplastic resin, such as a polycarbonate resin, a polyester resin, an acrylic resin and a polystyrene resin, or a thermosetting resin, such as a polyurethane resin and an epoxy resin, as the binder resin. Therefore, in the case where the surface of the charge transporting layer is negatively charged by corona discharge or roller discharge, such a problem arises that the surface of the photoreceptor is largely worn by electric impacts caused by discharge.
Various investigations have been made to solve the problem. For example, as described in JP-A-161279/1989, a polishing device for an electrophotographic photoreceptor is equipped in an electrophotographic apparatus, and the polishing device is used to provide a polishing amount on the surface of the photoreceptor of from 1 μm to 1.5 μm per 10,000 printing sheets to remove contaminants on the surface; as described in JP-A-75384/1994, a photoreceptor is used in such a manner that an ozone concentration around the photoreceptor is from 5 to 50 ppm, and a abrasion amount of the photoreceptor is 300 Å or less per 1,000 revolutions; and as described in JP-A-311470/1995, a contact pressure of a cleaning blade to a photoreceptor is set at a particular value, which is used to make an abrasion amount caused by a cleaning process of from 0.05 μm to 1.0 μm per 10,000 times cleaning, and a releasing agent having a number average domain diameter of from 0.1 μm to 1.1 μm is added to a toner.
However, the methods described in the foregoing literatures can control the abrasion amount in a non-contact charging method, such as corotron and scorotron, but substantially cannot control the abrasion amount because discharge stress is large in a contact charging method, represented by roller charging, to make the abrasion amount large. Consequently, they cause a problem in that the service life of the photoreceptor is shortened. Therefore, it has been demanded to provide an electrophotographic photoreceptor having a surface with higher strength.
Polysiloxane has been known as a resin that improves the strength of the surface layer. Polysiloxane receives attention as the surface layer of an electrophotographic photoreceptor because it has not only strength, transparency, insulation breakage resistance and photostability, but also such characteristics that are not owned by other resins, such as a low surface tension. For example, a polysiloxane resin is used as a copolymerization component or a polysiloxane resin is blended with other resins, as found in a thermosetting resin containing a polysiloxane resin (JP-A-238062/1986), a polysiloxane resin (JP-A-108260/1987), a thermosetting polysiloxane resin having silica gel, a urethane resin and a fluorine resin dispersed therein (JP-A-346356/1992) and a thermoplastic resin having a thermosetting polysiloxane resin dispersed therein (JP-A-4-273252/1992).
However, although polysiloxane has the foregoing excellent characteristics, it has extremely poor compatibility with other organic compounds, and therefore, it is not used as a binder constituting the surface layer solely by itself, but is used for modification of a binder by copolymerization or blending. Therefore, the characteristics of polysiloxane cannot be fully utilized.
In order to use a polysiloxane resin as a binder for constituting the surface layer solely by itself, the following proposals have been made. Polysiloxane, such as poly(hydrogenmethylsiloxane) is directly bonded to a charge transporting agent having an unsaturated bond by hydrosilylation to form a resin, which is used for forming the surface layer (JP-A-319353/1996); an inorganic thin film is formed by plasma CVD (JP-A-333881/1995); a thin film is formed by a sol-gel process (“Proceedings of IS&T's Eleventh International Congress on Advances in Non-Impact Printing Technologies”, pp. 57 to 59); and the surface layer is formed by using an organic silicon-modified hole transporting compound, which is formed by directly introducing a silicon compound having a hydrolyzable group into a charge transporting agent (JP-A-190004/1997).
Among the foregoing methods, those described in “Proceedings of IS&T's Eleventh International Congress on Advances in Non-Impact Printing Technologies”, p. 57 to 59 and JP-A-190004/1997 are receiving attention because siloxane forms a three-dimensional network to attain high mechanical strength.
However, in the case where a thin film formed by the sol-gel process or a product formed by crosslinking the organic silicon-modified hole transporting compound is used as the outermost layer of the photosensitive layer, filming, i.e., attachments accumulated on the surface of the photoreceptor, often occurs, and thus there are some cases where defects are formed on an image.